An electrophotography type image forming apparatus includes a high voltage power supply unit to supply power to a drum, a transfer belt, and a transfer output for paper. In the image forming apparatus, a mechanism for detecting an abnormal leakage due to corona discharge in the high voltage power supply unit, is adopted. For example, the image forming apparatus includes a control unit and a leakage detection block, and the control unit detects the abnormal leakage, based on a leakage detection signal that is input through a signal line from the leakage detection block.
Moreover, in recent years, a diffusion-based color image forming apparatus includes four stations including four drums corresponding to each color of Y (yellow), M (magenta), C (cyan), and Bk (Black). For example, the color image forming apparatus includes the control unit and four leakage detection blocks corresponding to the four stations. The control unit may detect the abnormal leakage based on the leakage detection signals that are input through the four signal lines from the four leakage detection blocks. In this case, the control unit may detect which station of the four stations generates the abnormal leakage.
In addition, the control unit of the image forming apparatus executes resistance detection in a transfer process unit, right before execution of a printing job. For example, in order to measure impedance within the transfer process unit, the control unit instructs a constant current mode with respect to the transfer process unit. In response thereto, a predetermined fixed current flows to the transfer process unit, the generated electromotive voltage is converted into a voltage that is detectable by the control unit, and an analog signal is output for monitoring the voltage. The control unit outputs a control signal for applying an appropriate transfer voltage based on the analog signal that is input through the signal line from the transfer process unit.